EIP-8025: should an execution client be required, optional, or recommended?

[frisitano]

Context

The current consensus-specs effectively require a CL to be paired with an execution client. EIP-8025 introduces a proof engine as an additional execution validity oracle — a second source the CL can consult to verify execution validity, using proofs rather than re-execution. This opens a concrete deployment class the spec has not formally taken a position on: a CL whose only execution validity oracle is a proof engine, with no execution client at all.

Client implementations are moving ahead of the spec: Lighthouse accepts --proof-engine-endpoint without --execution-endpoint today (eth-act/lighthouse#33). We should either codify that capability or explicitly rule it out, rather than letting the requirement erode silently.

Options

1. Required — status quo. Every CL must consult an EL for execution validity; the proof engine is a supplemental oracle. Simplest semantics; excludes a legitimate deployment class that EIP-8025 otherwise enables.
2. Optional — a CL may rely on a proof engine as its sole execution validity oracle, with no EL. Maximally permissive. Requires defining what a no-EL node can and cannot do.
3. Recommended — SHOULD-level guidance to run an EL alongside the proof engine, but permitted not to. Acknowledges operational reality while setting expectations.

References

• EIP-8025
• frisitano/consensus-specs#3 — internal fork PR proposing the change
• eth-act/lighthouse#33 — client-side precedent (CL works without EL)

[barnabasbusa]

I'd go with option 3.